Havn't read the thread TLDR, but I just had to add one more +1 to the pile of likes in this thread.
After being somewhat disappointed with the original Nighthawk, the Nighthawk Carbon is a breath of fresh air.
(Never owned either, but I often audition many top end / flagship headphones almost any time I like any day of the week in my lunch break near work)
It's the pads... sonically the two cans are the same. The NHs come with the "Classic" pads, which have the most radical tuning of the three pads offered; Carbons come with Boost and Ultra Suede. Which pads were on the Carbons you auditioned?
I have no idea

I actually wasn't aware that two different pads were available. Just wanted to leave the passing comment, spread the love, etc etc.